Background Gender-based violence (GBV) is a crucial global health problem among all age groups, including adolescents. This study describes incidences of GBV, as well as factors associated with sexual assault, among female adolescents in class six living in urban informal settlements in Nairobi, Kenya. Methods Study participants were interviewed using a structured survey instrument focusing on experiences of GBV, including emotional, physical, and sexual violence, and corresponding perpetrators, as well as gender attitudes, alcohol use, self-efficacy, and previous sexual experiences. Summary statistics and clustered bootstrap confidence intervals were calculated for social behaviors and violence rates. Stepwise logistic regression identified variables associated with an adolescent’s experience of sexual assault. Findings In this population 72% of adolescent girls reported being raped in the prior twelve months, with 111% of these rape victims reporting over five experiences. Among the 213% who report having had a boyfriend, 381% reported emotional, physical, and/or sexual intimate partner violence (IPV). Boyfriends were identified most often as perpetrators, accounting for 463% of reported lifetime rapes. Previous experience of physical (p = <0001) or emotional (p<0001) IPV and home violence (p<0001) were risk factors for being raped, while high self-efficacy (p<0001) was a protective factor. Interpretation Sexual assault and GBV are major challenges in this highly-disadvantaged population. Novel prevention efforts are needed for this age group, as prevention is often targeted at older adolescents. Prevention efforts should focus on assaults by perpetrators known to adolescents, especially boyfriends, and may need to account for the adolescents’ previous experience of, and exposure to, violence.
